The present invention relates to a method for controlling transmission power from a customer premise equipment device over a local loop of a digital subscriber line.
xDSL is a generic term for digital subscriber line equipment and services, including packet-based architectures, such as ADSL, HDSL, SDSL, VDSL, and RADSL. That is, x is the generic. xDSL technologies provide extremely high bandwidth over embedded twisted pair, copper cable plant. xDSL technologies offer great potential for bandwidth-intensive applications, such as Internet access, remote LAN access, video conferencing, and video-on-demand.
ADSL or asymmetric digital subscriber line services generally use existing unshielded twisted pair (UTP) copper wires from the telephone company""s central office to the subscriber""s premise, utilize electronic equipment in the form of ADSL modems at both the central office and the subscriber""s premise, send high-speed digital signals up and down those copper wires, and send more information one way than the other. The ADSL flavor of xDSL services is capable of providing a downstream bandwidth of about 1.5 Mbps-8 Mbps, and an upstream bandwidth of about 16 Kbps-64 Kbps with loop distances ranging from about 3.7 km-5.5 km. HDSL or high bit rate digital subscriber line services provide a symmetric, high-performance connection over a shorter loop, and typically require two or three copper twisted pairs. HDSL is capable of providing both upstream and downstream bandwidth of about 1.5 Mbps, over loop distances of up to about 3.7 km. SDSL or single line digital subscriber line services provide a symmetric connection that matches HDSL performance using a single twisted pair, but operating over a shorter loop of up to about 3.0 km. VDSL or very high bit rate digital subscriber line services are typically implemented in asymmetric form, as a very high speed variation on the ADSL theme over a very short loop. Specifically, target downstream performance is typically about 52 Mbps over UTP local loops of 300 m, 26 Mbps at 1,000 m, and 13 Mbps at 1,500 m. Upstream data rates in asymmetric implementations tend to range from about 1.6 Mbps to about 2.3 Mbps. Additionally, there is RADSL or rate adaptive digital subscriber line services. RADSL provides a dynamic connection that adapts to the length and quality of the line.
In the xDSL family of services, many xDSL themes, including ADSL, HDSL, SDSL, VDSL, and RADSL, utilize a packet-based approach that does away with the line-grabbing practice of circuit switched networks, such as ISDN (although ISDN service is a form of digital subscriber line). This packet-based approach is very advantageous in a variety of situations, such as high-speed data services, including high definition television or HDTV transmissions.
Of course, xDSL services, also commonly referred to as simply DSL or digital subscriber line services, are much more dependent on line conditions than traditional telephone services. Traditional telephone services typically use a bandwidth including frequencies up to about 3 kilohertz, while the DSL services utilize a bandwidth including frequencies up into the hundreds of kilohertz. While some local loops are in great condition for implementing DSL services, that is, the local loops have short to moderate lengths with minimal bridged taps and splices, many local loops are not as clean. For example, local loop length vary widely, for example, from as short as a few hundred meters to as long as several kilometers.
Further, sometimes the wire gauge for a local loop is not continuous over the length of the loop. That is, a portion of the local loop may be one wire gauge, while an adjacent portion of the local loop has a different wire gauge, with the two portions being spliced together. Still further, many existing local loops have one or more bridged taps. A bridged tap is a length of wire pair that is connected to a loop at one end and is unterminated at the other end. Sometimes, an existing local loop will have several bridged taps so that the telephone company may connect a customer to any one of the taps (while leaving the other taps unterminated). Tapped lines may allow the telephone company to better utilize its copper cable plant distribution. For example, a particular service area may include 25 residences. Because not all residences require multiple phone lines, there may be a total of about 30 or 35 local loops, with some of the loops having multiple bridged taps. As such, it may be possible for any one of the residences to order multiple line service, so long as only a few of the residences do so.
However, because DSL services have a strong dependence on line condition, splices and bridged taps may affect DSL services. If the line conditions are not excessively poor (loop length is not excessively long, while splices and taps are relatively minimal) increasing power for the DSL transmissions may be sufficient to provide adequate DSL services over the loop. It is to be appreciated that, however, simply increased transmission power alone does not always produce successful results.
In addition to loop lengths, number of splices, and number of bridged taps, there are other factors that are involved in providing a successful DSL solution. In addition to the conditions of the local loop itself affecting DSL implementation, crosstalk between local loops may also impair DSL service. For example, the central office side of a local loop is usually bundled into a binder group with other local loops. A binder group typically includes from as few as twenty-five pairs to as many as several hundred pairs. That is, a large number of pairs (loops) are bundled together into a binder group at the central office (or at a digital subscriber line access multiplexer or DSLAM, or at any other distribution point). As the binder group is routed away from the central distribution point, such as the central office, the loops branch out, with loops and small groups of loops departing from the binder group, until eventually, all of the loops are separated, similar to the way that a tree trunk branches out into smaller and smaller branches. On the customer end of the loop, DSL transmissions are sent from the end of the loop toward the central office (or DSLAM, or other distribution point). As the transmission travels toward the distribution end of the loop, the loop becomes bundled together with other loops. When the loops are bundled together, there is potential for crosstalk between different services of the same bundle or binder group. Accordingly, although increasing transmission power may sometimes reduce the effect the splices and bridged taps have on transmissions from the customer premise, the increased transmission power results in increased potential for crosstalk that may affect other loops when the transmission reaches the bundled loops.
Because a power control scheme is needed to assure that DSL transmissions are not underpowered and incapable of overcoming splices and bridged taps, an existing customer premise equipment device is capable of stepping up transmission power in the presence of excessive background noise (or back off when noise decreases). However, in an environment where each DSL service is introduced to a binder group one service at a time, the conventional scheme of measuring wideband frequency response and adjusting transmission power accordingly tends to create a so called race condition. In a race condition, the background noise causes each DSL service in a binder group to constantly boost transmission power a little bit at time. Eventually, all pairs will transmit at a fixed maximum power level. With all loop transmissions being fixed at the maximum power level, the effectiveness of the transmission power back-off functions are nullified. Further, because loop length and conditions vary widely, the race condition results in crosstalk from the better quality loops excessively interfering with the poorer quality loops.
For the foregoing reasons, there is a need for an improved DSL transmission power control method that overcomes the disadvantageous potential for crosstalk between different services in the same binder group that is associated with the race condition present in conventional power control techniques.
It is, therefore, an object of the present invention to provide a method for controlling transmission power from a customer premise equipment device over a local loop of a digital subscriber line that allows different loops in the same binder group to have different maximum power levels to reduce potential for crosstalk in the binder group.
In carrying out the above object, a method for controlling transmission power from a customer premise equipment device over a local loop of a digital subscriber line wherein a portion of the local loop is bundled with at least one other loop in a binder group is provided. The method comprises measuring a response of the local loop to a test signal, and determining a maximum power level for transmissions over the local loop from the customer premise equipment device. The maximum power level is based on the response so as to allow a different loop in the binder group to have a different maximum power level to reduce potential for crosstalk in the binder group when loops are brought together.
In a preferred embodiment, the method further comprises transmitting over the local loop with the customer premise equipment device generally at the maximum transmitting power level. Alternatively, the method further comprises determining a desired transmitting power level that is not more than the maximum transmitting power level, and transmitting over the local loop with the customer premise equipment device at the desired transmitting power level.
In one embodiment, measuring the response further comprises measuring a direct current response of the local loop to a direct current test signal. A suitable direct current test signal is a sealing current (also known as wetting current) that is applied to a loop for the purpose of preventing transmission degradation due to the oxidation of wire splices. Of course, the sealing current may be continuous or periodically applied. Preferably, measuring further comprises measuring a frequency response of the local loop to a frequency test pattern signal. The frequency test pattern signal is preferably constructed to allow detection of a bridged tap in the local loop. Further, the frequency test pattern signal is preferably constructed to allow detection of a loaded loop. A loaded loop is a loop that is loaded with an inductance to increase low frequency gain, at the expense of high frequency gain, to improve quality of traditional telephone service, but making DSL implementation a bit more difficult.
In one implementation, the local loop has a first end at the customer premise equipment device and a second end at a provider equipment device. Measuring the response and determining the maximum power level will occur at the customer premise equipment device at the local loop such that maximum power levels among different loops in the same binder group are not directly coordinated. Advantageously, each customer premise equipment device may draw conclusions about the conditions of its local loop, and determine a maximum power level accordingly. Although the maximum power levels among the different local loops are not directly coordinated, using the same maximum power level determination technique at each customer premise equipment device effectively reduces crosstalk potential when the loops are bundled together. In the alternative, determinating the maximum power level may occur at the provider equipment end of the local loop to allow coordination of maximum power levels among different local loops in the same binder group. In this alternative embodiment, maximum power levels for the different local loops are directly dependent on each other to provide even more certainty that the potential for crosstalk is substantially minimized among local loops in the same binder group.
Further, in carrying out the present invention, a method for controlling transmission power from a customer premise equipment device over a local loop of a digital subscriber line comprises measuring a relative resistance of the local loop. The method further comprises determining a maximum power level for transmission over the local loop from the customer premise equipment device based on the relative resistance. Preferably, the method further comprises measuring a frequency response of the local loop to a frequency test pattern, and the maximum power level is further based on the frequency response.
Still further, in carrying out the present invention, the method for controlling transmission power from a customer premise equipment device over a local loop of a digital subscriber line comprises estimating the loop length by measuring a response of the local loop to an essentially direct current test signal. Although a direct current test signal is preferred, it is appreciated that any test signal having a sufficiently low frequency to avoid frequency response characteristics associated with unterminated line ends may be sufficient for estimating loop length. The method further comprises determining a maximum power level for transmissions over the local loop from the customer premise equipment device based on the estimated loop length.
In one embodiment, the test signal is a sealing current. Preferably, the method further comprises measuring a frequency response of the local loop to a frequency test pattern, and the maximum power level is further based on the frequency response.
Even further, in carrying out the present invention, a customer premise equipment device for a local loop of a digital subscriber line is provided. The customer premise equipment device comprises a transmission unit including a transceiver, a detector, and control logic. The detector measures a response indicative of a relative resistance of the local loop. The control logic is configured to process the response and determine a maximum power level for transmissions over the loop from the transceiver.
The advantages associated with embodiments of the present invention are numerous. For example, embodiments of the present invention determine a maximum power level for transmissions over the local loop in such a way that potential for crosstalk among loops of the same binder group is substantially reduced. The maximum power levels for the local loops may be coordinated with each other, or (preferably) may be not directly coordinated but preferably based on the same rules so that potential for crosstalk is substantially reduced. In one embodiment, the maximum power level for. transmissions over the local loop is based on the measured response of the local loop to a test signal. In a particular implementation, the maximum power level is based on a measured relative resistance of the local loop (relative to resistance of the other loops). Further, in another embodiment, loop length is estimated by measuring a response of the local loop to an essentially direct current test signal, and the maximum power level is based on the estimated loop length.
Advantageously, although different techniques may be utilized to estimate line conditions, such as loop length, and the presence of splices or taps, embodiments of the present invention determine a maximum power level for transmission over a local loop in such a way that different local loops have different corresponding maximum transmission power levels such that potential for crosstalk when the loops are bundled together in the binder group is substantially reduced. Particularly, because the different local loops may extend over different lengths and conditions prior to reaching the binder group, signal noise such as attenuation and distortion may vary from loop to loop where each loop meets the other at the binder group. As such, in accordance with the present invention, setting a maximum power level for transmissions from the customer premise equipment device may compensate for varying line conditions reducing crosstalk potential because the different loops have appropriate maximum power levels to result in signals having similar or compatible power levels alongside each other in a binder group.
The above object and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.